Mobile radio operates with electromagnetic waves in the decimeter range. A monopole is a linear antenna trace which can be formed in or on the window pane formed with the antenna and which normally is set into a window frame or is otherwise mounted on the metallic body of the vehicle. The pane itself can be a single pane or a composite pane made up of a laminate, e.g. in the case of safety glass.
The antenna trace can be printed, for example, on the glass and can be built up, if desired, galvanically, or can be incorporated in the glass as a wire trace.
A monopole whose length is a quarter of the wavelength is generally referred to as a quarter lambda monopole and, since the long wavelength with which the present application is concerned has been designed at L and the short wavelength as K, the quarter lambda monopoles thereof will have lengths of L/4 and K/4 respectively and will be referred to as L/4 and K/4 monopoles respectively.
The transmission characteristics and, conversely, the reception characteristics of quarter lambda monopoles are excellent with respect to the wide angle of transmission and reception (high access angle) and are characterized as well by a relatively high vertical access angle. They, therefore, are highly useful for mobile radio and thus in the mobile radio range the use of L/4 and K/4 monopoles is known.
However, with such known antenna panes, the L/4 and K/4 monopoles generally are provided as independent antennas which are not conductively interconnected. They are separately operated. In the case of L wavelength mobile radio, the L/4 monopole is switched into service and for K wavelength mobile radio transmission and reception, the K/4 monopole is used.
The inductive and/or capacitive alternation of the two monopoles does not pose a problem.
The transmission characteristic of a quarter lambda monopole is clearly defined for an arrangement of a quarter lambda monopole above an endless fully conductive surface, generally referred to ground or ground plane and the same applies reciprocally for the receiving characteristic.
In practice, however, where the antenna is a rod and the body of the vehicle functions as a ground plane or ground, it has been found to be desirable to simulate the ground by a radial constituting an antenna element whose length is determined by the wavelength and which is in inductive or capacitive exchange with the vehicle body.
The radials of an antenna on a window pane generally run parallel to a metallic edge of the window opening.
Such systems have been found to be very satisfactory for mobile radio. However, the independent arrangement of two antennas with their respective quarter lambda monopoles requires special treatment in the path from the transmitter to the antenna and from the antenna to the receiver and has created problems with such connections. Problems also have arisen in modern vehicle fabrication techniques where the antenna panes must be automatically mounted in the vehicle body, with respect to the running of the lines between the transmitter and receiver and the window antenna.
For the reception of classical shortwave signals, whose wavelengths are substantially longer than the electromagnetic waves of modern mobile radio, it is known to operate with crossed linear antennas (see British Patent document GB 460 570) whose cross arm to both sides of the crossing point are of different lengths and on one side and the other of the crossover are in resonance with crossing waves of the shortwave spectrum, like lambda half dipoles. They are not, however, separately driven in the sense previously described.
This antenna is not provided with radials of the type mentioned above and the application of the principles of this system to window antennas which are set into motor vehicle bodies and for mobile radio is not described nor does the document contain any teaching as to how the dipoles can be matched to wavelengths which are suitable for mobile radio.
Window antennas for motor vehicles which have monopoles of different lengths for different wavelengths and electronically interconnected are described in Japanese Patent Document JP A 62-43905 and U.S. Pat. No. 4,749,989, without any reference to radials. These antennas are not suitable either for mobile radio in a dual-band operation.